In French, the term la rentrée refers to the period of the year between late August and late September when, after the summer holidays, life begins to return to normal. Sometimes it's qualified with an adjective. Thus, la rentrée scolaire means the start of the school year, la rentrée universitaire the start of university term and so on.

In politics, la rentrée politique comes in late August and marks the end of a fortnight or three-week trêve estivale, the summer truce between parties, when they focus more closely on internal issues, policy, organisation, disintegration and so forth. Often, the end of the period of ceasefire is signalled by each party's université d'été, although the Socialists are in such disarray and hard-up that their université was reduced to a séminaire. By the same token, Les Républicains spent most of their time focusing on the upcoming Senate election and trying to avoid pre-leadership campaign stand-off (and failing).

Of the opposition parties, only Jean-Luc Mélenchon’s La France Insoumise made much noise about their Amphis de l’été, held at the Université de Marseille, where their leader restated his claim that LFI are now the only left-wing opposition to Macron and promised the government a difficult autumn…

Which brings us to the rentrée sociale - strike season. With the return to work comes the opportunity for the trades unions to organise industrial action to show their disapproval of government reforms and this year, with the passage of the enabling bill though parliament in August, allowing the Philippe administration to enact labour law reforms by decree, is no exception. Thus, on 12 September, there were strikes across the country led by the Confédération Générale du Travail (CGT), one of the French trade union federations.

I say one of, because in France they proliferate, from the moderate and reformist Confédération Française Démocratique du Travail (CFDT), to the more confrontational Force Ouvrière (FO) and the CGT, along with, in more recent times, a raft of other national or regional federations. And therein lies part of the problem for those contesting the Macron-Philippe government’s plans. When the left-wing newspaper Libération publishes an editorial criticising the les syndicats for their weakness, poor leadership and lack of unity, you know they’re in trouble. It isn’t that other unions agree with Macron’s reforms, but finding common ground has proved difficult. It's one thing to oppose the government's reforms, but as Libé points out, something has to change. Defending a specific French 'social model' while sustaining the sort of structural unemployment that persists in France is no longer adequate. By the same token, none of the other unions is unhappy to see its frères-ennemis riven by internal conflicts and struggling to hold onto its membership.

Philippe Martinez, head of the CGT, claimed that the strikes on 12 September were a success – well, he would. According to the CGT, some 500,000 people came out to demonstrate across the country, but the official figures are closer to 220,000, and while a second strike has been called for and other unions have decided to back one-day industrial action, it’s not clear from the early exchanges that the strike season will end up with a massive nationwide general strike.

The usual pattern is this. The government introduces legislation. Over the summer, the unions mull over their response. In September we get the opening salvoes and, if there is a reasonable response from the workforce, by October we’re into impressive waves of strikes. Sometimes, one even gets the sense that the country really is behind the striking unions. In 1995, for example, when the country was crippled by strikers opposed to the Juppé government, one really got the impression that the wider public supported the movement.

By the time we get to widespread strikes in October and November, perhaps a few blockaded ports, oil refineries and so on, then the government, more often than not, backs down and nothing, or very little changes. Now, the union of fairground workers (les forains) are threatening just such action… but the Philippe government does not appear to be willing budge.

The next key dates are Thursday 21 September, when the CGT has called for another day of action, and then 23 September, when Mélenchon plans to march in Paris.

And therein lies the rub.

The CGT’s call for a second day of action is a direct response to what it sees as a threat to its position, not by a rival union but by a political party. Historically, the CGT was always closer to the Communist party and Mélenchon’s relations with them are strained at the best of times. The announcement the other day that he will not be attending this weekend’s Fête de l’Humanité has only served to underline their estrangement. For his part, Mélenchon has made it no secret that he wants LFI to become the spearhead of unified left-wing.

For the gauche de la gauche, then, la rentrée sociale poses its own problems. Commentators will be watching very closely next Thursday and Saturday to see what sort of turnout each attracts. In the past, Mélenchon has relied on the Communists to mobilise mass street demonstrations in support of his presidential campaigns. But a massive turnout on 23 September would represent an enormous fillip to him and to La France Insoumise by themselves. It isn’t just about opposing the Macron-Philippe government.

The government will, of course, be watching developments very closely. At the same time, on 24 September, they will be hoping for good news from the partial renewal of the upper house, the French Senate, ahead of la rentrée parlementaire. And I'll come to that next week.